1. Field of the Invention:
The present invention relates to a degassing vessel for the vacuum treatment of liquid steel, which vessel consists of lower, middle and upper parts. The vessel has a metal jacket, lined on the inside of the vessel with refractory material. Also, the middle part of the vessel, in the portion facing the lower part, has a cylindrical shape having the same radius as the lower part. There is at least one snorkel tube in the floor of the bottom part, which tube is immersed in the melt of a ladle located therebeneath. Also, in the middle part, there is a heater rod oriented at a right angle to the center axis, as well as a charging device. In the upper part, there is a sight hole and an exhaust gas connection, the exhaust gas connection being connected to a vacuum system and oriented at a right angle to the center axis.
2. Background Information:
Degassing vessels such as those described above are generally used for the degassing of liquid steel to achieve extremely low carbon concentrations. Known are two processes which are applied to portions of the liquid steel. In one process, the liquid steel is sucked via a blowpipe into the vacuum chamber, and is discharged through the same blowpipe back into the ladle underneath. In the other process for handling a quantity of liquid steel, the so-called continuous process, the liquid steel is sucked in through a snorkel tube and is continuously returned to the ladle via a second snorkel tube.
To achieve the highest possible production rate, and to avoid thermal losses during the treatment of the liquid steel, the steelmaker usually finds it advantageous to keep the treatment time for the steel as brief as possible. To control and regulate the temperature of the melt and of the furnace, heating devices are located in the vicinity of the center of the vacuum vessel.
As an example, German Patent Publication Published for Opposition Purposes No. 15 33 933 essentially discloses a vacuum chamber with a refractory lining in a vacuum-tight steel casing, which forms a flat hearth in a lower portion, into which a blowpipe for the intake and discharge of the portion of a melt to be treated empties, and which is tapered so that it narrows at the top. In the upper part, there is a heater to preheat the chamber and to keep the melt hot. The chamber is closed by means of a dome-shaped cover made of refractory material with an opening for connection to the vacuum pump system.
It is also known to use vessels which, without any conical taper, are designed to be essentially completely cylindrical and, in the vicinity of the vessel head, have an exhaust gas connection oriented generally at a right angle with respect to the center axis.
Generally, in degassing vessels, particles are entrained by the degassing current. The gas then strikes the surfaces which direct its flow, and individual particles accumulate at these points, on the surfaces. Generally, there tends to be a rather large accumulation of such particles above the heater rod, on the head surface of the degassing vessel, which surface acts as a deflector plate. There, the individual particles form suspended lobes, arranged in sheets. These suspended lobes essentially have a solid consistency, and after the lobes reach a certain size, they break away from the adhering surface at irregular intervals. These broken-off formations, also called skull, fall into the current of liquid steel and thence have a negative effect on the composition of the liquid steel. As the broken-off formations of skull travel through the vacuum vessel, they generally represent a great danger for the heater rods, which generally consist of graphite. Broken fragments of these heater rods can thence result in scrapped melts for steel grades with a low carbon content, on account of unplanned or unintended carburization.